It is often necessary in semiconductor processing to fill a high aspect ratio gap with insulating material. As device dimensions shrink and thermal budgets are reduced, void-free filling of high aspect ratio spaces (AR>3.0:1) becomes increasingly difficult due to limitations of existing deposition processes. The deposition of doped or undoped silicon dioxide assisted by high density plasma CVD, a directional (bottom-up) CVD process, is the method currently used for high aspect ratio (AR) gap-fill. Evolving semiconductor device designs and dramatically reduced feature sizes have resulted in several applications where High Density Plasma (HDP) processes are challenged in filling the high aspect ratio structures (AR>7:1) using existing technology (see, for example, U.S. Pat. No. 6,030,881, which is hereby incorporated by reference herein for all purposes). For structures representative of 65 nm and 45 nm technology nodes, engineering the gap-fill process becomes structure dependent, hence the process needs to be reoptimized, a task of considerable complexity, every time a new structure needs to be filled.
Chemical vapor deposition (CVD) has traditionally been the method of choice for depositing conformal silicon dioxide films. However, as design rules continue to shrink, the aspect ratios (depth to width) of features increase, and traditional CVD techniques can no longer provide adequately conformal films in these high aspect ratio features.
An alternative to CVD is atomic layer deposition (ALD). ALD methods involve self-limiting adsorption of reactant gases and can provide thin, conformal dielectric films within high aspect ratio features. Atomic Layer Deposition (ALD) is a method with which extremely conformal films can be deposited. ALD methods have been developed for the deposition of SiO2 film. Because the ALD approach deposits only one atomic layer per cycle, it is extremely slow. Recently a method has emerged for self-limiting conformal film growth of multiple SiO2 layers per deposition cycle. See, Hausmann, D.; Becker, J.; Wang, S.; Gordon, R. G. Science 2002, 298, 402 and Miller, K. A.; John, C.; Zhang, K. Z.; Nicholson, K. T.; McFeely, F. R.; Banaszak Holl, M. M. Thin Solid Films 2001, 397, 78.
An ALD-based dielectric deposition technique typically involves adsorbing a metal containing precursor onto the substrate surface, then, in a second procedure, introducing a silicon oxide precursor gas. The silicon oxide precursor gas reacts with the adsorbed metal precursor to form a thin film of metal-doped silicon oxide. One drawback, however, to ALD is that the deposition rates are very low. Films produced by ALD are also very thin (i.e., about one monolayer); therefore, numerous ALD cycles must be repeated to adequately fill a gap feature. These processes are unacceptably slow in many manufacturing environment applications.
A related technique, referred to as rapid vapor deposition (RVD) processing, is another alternative. RVD is similar to ALD in that reactant gases are introduced alternately over the substrate surface, but in RVD the silicon oxide film can grow more thickly. Thus, RVD methods allow for rapid film growth similar to using CVD methods but with the film conformality of ALD methods.
It is desirable to improve the performance of RVD techniques, leading to improved film growth rate, greater self-limiting film thickness, reduced aluminum (or other catalyst) content, and decreased film moisture and OH content. Additionally, it is desirable to use precursors with lower melting points and higher volatility.